Microwave ablation instrument with flexible antenna assembly and method

ABSTRACT

A flexible microwave antenna assembly for a surgical ablation instrument capable of conforming to a tissue surface for ablation thereof. The ablation instrument includes a transmission line having a proximal portion suitable for connection to an electromagnetic energy source. The antenna assembly includes a flexible antenna coupled to the transmission line for radially generating an electric field sufficiently strong to cause tissue ablation. A flexible shield device is coupled to the antenna to substantially shield a surrounding area of the antenna from the electric field radially generated therefrom while permitting a majority of the field to be directed generally in a predetermined direction. A flexible insulator is disposed between the shield device and the antenna which defines a window portion enabling the transmission of the directed electric field in the predetermined direction. The antenna, the shield device and the insulator are formed for selective manipulative bending thereof, as a unit, to one of a plurality of contact positions to generally conform the window portion to the biological tissue surface to be ablated.

RELATED APPLICATIONS

[0001] This application is a continuation of U.S. patent applicationSer. No. 09/484,548, filed Jan. 18, 2000, entitled “A MICROWAVE ABLATIONINSTRUMENT WITH FLEXIBLE ANTENNA ASSEMBLY AND METHOD,” a copy of whichis hereby incorporated herein by reference, in its entirety.

BACKGROUND OF THE INVENTION

[0002] 1. Field of Invention

[0003] The present invention relates, generally, to ablation instrumentsystems that use electromagnetic energy in the microwave frequencies toablate internal bodily tissues, and, more particularly, to antennaarrangements and instrument construction techniques that direct themicrowave energy in selected directions that are relatively closelycontained along the antenna.

[0004] 2. Description of the Prior Art

[0005] It is well documented that atrial fibrillation, either alone oras a consequence of other cardiac disease, continues to persist as themost common cardiac arrhythmia. According to recent estimates, more thantwo million people in the U.S. suffer from this common arrhythmia,roughly 0.15% to 2.0% of the population. Moreover, the prevalence ofthis cardiac disease increases with age, affecting nearly 8% to 17% ofthose over 60 years of age.

[0006] Atrial arrhythmia may be treated using several methods.Pharmacological treatment of atrial fibrillation, for example, isinitially the preferred approach, first to maintain normal sinus rhythm,or secondly to decrease the ventricular response rate. Other forms oftreatment include chemical cardioversion to normal sinus rhythm,electrical cardioversion, and RF catheter ablation of selected areasdetermined by mapping. In the more recent past, other surgicalprocedures have been developed for atrial fibrillation, including leftatrial isolation, transvenous catheter or cryosurgical ablation of Hisbundle, and the Corridor procedure, which have effectively eliminatedirregular ventricular rhythm. However, these procedures have for themost part failed to restore normal cardiac hemodynamics, or alleviatethe patient's vulnerability to thromboembolism because the atria areallowed to continue to fibrillate. Accordingly, a more effectivesurgical treatment was required to cure medically refractory atrialfibrillation of the heart.

[0007] On the basis of electrophysiologic mapping of the atria andidentification of macroreentrant circuits, a surgical approach wasdeveloped which effectively creates an electrical maze in the atrium(i.e., the MAZE procedure) and precludes the ability of the atria tofibrillate. Briefly, in the procedure commonly referred to as the MAZEIII procedure, strategic atrial incisions are performed to preventatrial reentry and allow sinus impulses to activate the entire atrialmyocardium, thereby preserving atrial transport functionpostoperatively. Since atrial fibrillation is characterized by thepresence of multiple macroreentrant circuits that are fleeting in natureand can occur anywhere in the atria, it is prudent to interrupt all ofthe potential pathways for atrial macroreentrant circuits. Thesecircuits, incidentally, have been identified by intraoperative mappingboth experimentally and clinically in patients.

[0008] Generally, this procedure includes the excision of both atrialappendages, and the electrical isolation of the pulmonary veins.Further, strategically placed atrial incisions not only interrupt theconduction routes of the common reentrant circuits, but they also directthe sinus impulse from the sinoatrial node to the atrioventricular nodealong a specified route. In essence, the entire atrial myocardium, withthe exception of the atrial appendages and the pulmonary veins, iselectrically activated by providing for multiple blind alleys off themain conduction route between the sinoatrial node to theatrioventricular node. Atrial transport function is thus preservedpostoperatively as generally set forth in the series of articles: Cox,Schuessler, Boineau, Canavan, Cain, Lindsay, Stone, Smith, Corr, Change,and D'Agostino, Jr., The Surgical Treatment Atrial Fibrillation (pts.1-4), 101 THORAC CARDIOVASC SURG., 402-426, 569-592 (1991).

[0009] While this MAZE III procedure has proven effective in ablatingmedically refractory atrial fibrillation and associated detrimentalsequelae, this operational procedure is traumatic to the patient sincesubstantial incisions are introduced into the interior chambers of theheart. Consequently, other techniques have thus been developed tointerrupt and redirect the conduction routes without requiringsubstantial atrial incisions. One such technique is strategic ablationof the atrial tissues through ablation catheters.

[0010] Most approved ablation catheter systems now utilize radiofrequency (RF) energy as the ablating energy source. Accordingly, avariety of RF based catheters and power supplies are currently availableto electrophysiologists. However, radio frequency energy has severallimitations including the rapid dissipation of energy in surface tissuesresulting in shallow “burns” and failure to access deeper arrhythmictissues. Another limitation of RF ablation catheters is the risk of clotformation on the energy emitting electrodes. Such clots have anassociated danger of causing potentially lethal strokes in the eventthat a clot is dislodged from the catheter.

[0011] As such, catheters which utilize electromagnetic energy in themicrowave frequency range as the ablation energy source are currentlybeing developed. Microwave frequency energy has long been recognized asan effective energy source for heating biological tissues and has seenuse in such hyperthermia applications as cancer treatment and preheatingof blood prior to infusions. Accordingly, in view of the drawbacks ofthe traditional catheter ablation techniques, there has recently been agreat deal of interest in using microwave energy as an ablation energysource. The advantage of microwave energy is that it is much easier tocontrol and safer than direct current applications and it is capable ofgenerating substantially larger lesions than RF catheters, which greatlysimplifies the actual ablation procedures. Such microwave ablationsystems are described in the U.S. Pat. Nos. 4,641,649 to Walinsky;5,246,438 to Langberg; 5,405,346 to Grundy, et al.; and 5,314,466 toStern, et al, each of which is incorporated herein by reference.

[0012] Most of the existing microwave ablation catheters contemplate theuse of longitudinally extending helical antenna coils that direct theelectromagnetic energy in a radial direction that is generallyperpendicular to the longitudinal axis of the catheter although thefields created are not well constrained to the antenna itself. Althoughsuch catheter designs work well for a number of applications, such asradial output, they are inappropriate for use in precision surgicalprocedures. For example, in MAZE III surgical procedures, very preciseand strategic lesions must be formed in the heart tissue which theexisting microwave ablation catheters are incapable of delivering.

[0013] Consequently, microwave ablation instruments have recently beendeveloped which incorporate microwave antennas having directionalreflectors. Typically, a tapered directional reflector is positionedperipherally around the microwave antenna to direct the waves toward andout of a window portion of the antenna assembly. These ablationinstruments, thus, are capable of effectively transmittingelectromagnetic energy in a more specific direction. For example, theelectromagnetic energy may be transmitted generally perpendicular to thelongitudinal axis of the catheter but constrained to a selected angularsection of the antenna, or directly out the distal end of theinstrument. Typical of these designs are described in the U.S. patentapplication Ser. Nos. 09/178,066, filed Oct. 23, 1998; and 09/333,747,filed Jun. 14, 1999, each of which is incorporated herein by reference.

[0014] In these designs, the of the microwave antenna is preferablytuned assuming contact between the targeted tissue and a contact regionof the antenna assembly extending longitudinally adjacent to the antennalongitudinal axis. Hence, should a portion of, or substantially all of,the exposed contact region of the antenna not be in contact with thetargeted tissue during ablation, the adaptation of the antenna will beadversely changed and the antenna will be untuned. As a result, theportion of the antenna not in contact with the targeted tissue willradiate the electromagnetic radiation into the surrounding air. Theefficiency of the energy delivery into the tissue will consequentlydecrease which in turn causes the penetration depth of the lesion todecrease.

[0015] This is particularly problematic when the tissue surfaces aresubstantially curvilinear, or when the targeted tissue for ablation isdifficult to access. Since these antenna designs are generallyrelatively rigid, it is often difficult to maneuver substantially all ofthe exposed contact region of the antenna into abutting contact againstthe targeted tissue. In these instances, several ablation instruments,having antennas of varying length and shape, may be necessary tocomplete just one series of ablations.

SUMMARY OF THE INVENTION

[0016] Accordingly, a flexible microwave antenna assembly is providedfor a surgical ablation instrument adapted to ablate a surface of abiological tissue. The ablation instrument includes a transmission linehaving a proximal portion suitable for connection to an electromagneticenergy source. The antenna assembly includes a flexible antenna coupledto the transmission line for radially generating an electric fieldsufficiently strong to cause tissue ablation. A flexible shield deviceis coupled to the antenna to substantially shield a surrounding area ofthe antenna from the electric field radially generated therefrom whilepermitting a majority of the field to be directed generally in apredetermined direction. A flexible insulator is disposed between theshield device and the antenna which defines a window portion enablingthe transmission of the directed electric field in the predetermineddirection. In accordance with the present invention, the antenna, theshield device and the insulator are formed for selective manipulativebending thereof, as a unit, to one of a plurality of contact positionsto generally conform the window portion to the biological tissue surfaceto be ablated.

[0017] In one configuration, a longitudinal axis of the antenna isoff-set from a longitudinal axis of the insulator to position theantenna substantially proximate to and adjacent the window portion. Theshield device is in the shape of a semi-cylindrical shell having alongitudinal axis generally co-axial with a longitudinal axis of theinsulator.

[0018] In another embodiment, the insulator defines a receiving passageformed for sliding receipt of the antenna longitudinal therein duringmanipulative bending of the antenna assembly. Moreover, a polyimide tubedevice may be positioned in the receiving passage proximate the distalend of the antenna. The tube provides a bore formed and dimensionedsliding longitudinal reciprocation therein of at least the distal end ofthe antenna.

[0019] Another embodiment of the present invention provides anelongated, bendable, retaining member adapted for longitudinal couplingtherealong to the insulator. This bendable retaining member enables theinsulator to retain the one contact position after manipulative bendingthereof for the conformance of the window portion to the biologicaltissue surface to be ablated. The retaining member is preferablydisposed longitudinally along the insulator, and on one the of theshield device, while the antenna is preferably disposed on an oppositeside of the shield device, longitudinally along the insulator, andbetween the shield device and the window portion.

[0020] In another aspect of the present invention provides a microwaveablation instrument, adapted to ablate a surface of a biological tissue,is provided having a handle member formed for manual manipulation of theablation instrument. An elongated transmission line is provided coupledto the handle member. A proximal portion of the transmission line issuitable for connection to an electromagnetic energy source. Theablation instrument further includes a flexible antenna assembly coupledto the handle member which is formed for selective manipulative bendingthereof. The antenna assembly includes a flexible antenna coupled to thetransmission line for radially generating an electric field sufficientlystrong to cause tissue ablation. A flexible shield device of the antennaassembly is employed to substantially shield a surrounding radial areaof the antenna from the electric field radially generated therefrom,while permitting a majority of the field to be directed generally in apredetermined direction. A flexible insulator is disposed between theshield device and the antenna, and defines a window portion enabling thetransmission of the directed electric field in the predetermineddirection. The antenna, the shield device and the insulator are formedfor selective manipulative bending thereof, as a unit, to one of aplurality of contact positions to generally conform the window portionto the biological tissue surface to be ablated.

[0021] In this configuration, the ablation instrument may include abendable, malleable shaft having a proximal portion coupled to thehandle member, and an opposite a distal portion coupled to the antennaassembly. The shaft is preferably a semi-rigid coaxial cable, but mayalso include a tubular shaft where the transmission line may be disposedtherethrough from the proximal portion to the distal portion thereof.The shaft is preferably conductive having a distal portion conductivelycoupled to the proximal end of the shield device, and another portionconductively coupled to the outer conductor of the transmission line.

[0022] In another embodiment, a restraining sleeve is adapted to limitthe bending movement of the bendable antenna assembly at the conductivecoupling between the shield device and the shaft. The restraining sleeveis formed and dimensioned to extend peripherally over the conductivecoupling to limit the bending movement in a predetermined direction tomaintain the integrity of conductive coupling. The restraining sleeveincludes a curvilinear transverse cross-sectional dimension extendingpast the conductive coupling longitudinally therealong by an amountsufficient to maintain the integrity.

[0023] In still another configuration, an elongated grip member isincluded having a distal grip portion and an opposite proximal portioncoupled to a distal portion of the antenna assembly. The grip member andthe handle member cooperate to selectively bend the antenna assembly andselectively urge the window portion in abutting contact with thebiological tissue surface to be ablated. The gripping member ispreferably provided by an elongated flexible rod having a diametersmaller than a diameter of the insulator. A longitudinal axis of theflexible rod is off-set from the longitudinal axis of the insulator toposition the rod in general axial alignment with the antenna, andadjacent the window portion.

[0024] In still another aspect of the present invention, a method isprovided for ablating medically refractory atrial fibrillation of theheart including the step of providing a microwave ablation instrumenthaving a flexible antenna assembly adapted to generate an electric fieldsufficiently strong to cause tissue ablation. The antenna assemblydefines a window portion enabling the transmission of the electric fieldtherethrough in a predetermined direction. The method further includesselectively bending and retaining the flexible antenna assembly in oneof a plurality of contact positions to generally conform the shape ofthe window portion to the targeted biological tissue surface to beablated, and manipulating the ablation instrument to strategicallyposition the conformed window portion into contact with the targetedbiological tissue surface. The next step includes forming an elongatedlesion in the targeted biological tissue surface through the generationof the electric field by the antenna assembly.

[0025] These bending, manipulating and generating events are preferablyrepeated to form a plurality of strategically positioned ablationlesions. Collectively, these lesions are formed to create apredetermined conduction pathway between a sinoatrial node and anatrioventricular node of the heart.

BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The assembly of the present invention has other objects andfeatures of advantage which will be more readily apparent from thefollowing description of the best mode of carrying out the invention andthe appended claims, when taken in conjunction with the accompanyingdrawing, in which:

[0027]FIG. 1 is a diagrammatic top plan view of a microwave ablationinstrument system with a bendable directional reflective antennaassembly constructed in accordance with one embodiment of the presentinvention.

[0028]FIG. 2 is an enlarged, fragmentary, top perspective view of theantenna assembly of FIG. 1 mounted to a distal end of a handle member ofthe ablation instrument.

[0029]FIG. 3 is an enlarged, fragmentary, top perspective view of theantenna assembly of FIG. 1 illustrated in a bent position to conform toa surface of the tissue to be ablated.

[0030]FIG. 4 is an enlarged, fragmentary, top perspective view of theantenna assembly of FIG. 2 illustrated in another bent position toconform to a surface of the tissue to be ablated.

[0031]FIG. 5 is an enlarged, fragmentary, top plan view of the antennaassembly of FIG. 2 illustrating movement between a normal position(phantom lines) and a bent position (solid lines).

[0032]FIG. 6 is a fragmentary side elevation view of the antennaassembly of FIG. 5.

[0033]FIG. 7 is an enlarged, front elevation view, in cross-section, ofthe antenna assembly taken substantially along the plane of the line 7-7in FIG. 6.

[0034]FIG. 8 is an enlarged, fragmentary, side elevation view of theantenna assembly of FIG. 2 having a restraining sleeve coupled thereto.

[0035]FIG. 9 is an enlarged, front elevation view, in cross-section, ofthe antenna assembly taken substantially along the plane of the line 9-9in FIG. 8.

[0036]FIG. 10 is a diagrammatic top plan view of an alternativeembodiment microwave ablation instrument system constructed inaccordance with one embodiment of the present invention.

[0037]FIG. 11 is a reduced, fragmentary, top perspective view of theantenna assembly of FIG. 10 illustrated in a bent position to conform toa surface of the tissue to be ablated.

[0038]FIG. 12 is a reduced, fragmentary, top perspective view of analternative embodiment antenna assembly of FIG. 10 having a flexiblehandle member.

DETAILED DESCRIPTION OF THE INVENTION

[0039] While the present invention will be described with reference to afew specific embodiments, the description is illustrative of theinvention and is not to be construed as limiting the invention. Variousmodifications to the present invention can be made to the preferredembodiments by those skilled in the art without departing from the truespirit and scope of the invention as defined by the appended claims. Itwill be noted here that for a better understanding, like components aredesignated by like reference numerals throughout the various Figures.

[0040] Turning now to FIGS. 1-4, a microwave ablation instrument,generally designated 20, is provided which is adapted to ablate asurface 21 of a biological tissue 22. The ablation instrument 20includes a handle member 23 formed to manually manipulate the instrumentduring open surgery. An elongated transmission line 25 is providedcoupled to the handle member 23 at a distal portion thereof, and havinga proximal portion suitable for connection to an electromagnetic energysource (not shown). The ablation instrument 20 further includes aflexible antenna assembly, generally designated 26, coupled to thehandle member 23 and to the transmission line 25 to generate an electricfield. The antenna assembly 26 is adapted to transmit an electric fieldout of a window portion 27 thereof in a predetermined directionsufficiently strong to cause tissue ablation. The antenna assembly isfurther formed for selective manipulative bending to one of a pluralityof contact positions (e.g., FIGS. 3 and 4) to generally conform thewindow portion 27 to the biological tissue surface 21 to be ablated.

[0041] More specifically, the flexible antenna assembly 26 includes aflexible antenna 28 coupled to the transmission line 25 for radiallygenerating the electric field substantially along the longitudinallength thereof. A flexible shield device 30 substantially shields asurrounding radial area of the antenna wire 28 from the electric fieldradially generated therefrom, while permitting a majority of the fieldto be directed generally in a predetermined direction toward the windowportion 27. A flexible insulator 31 is disposed between the shielddevice 30 and the antenna 28, and defines the window portion 27 enablingthe transmission of the directed electric field in the predetermineddirection. The antenna 28, the shield device 30 and the insulator 31 areformed for selective manipulative bending thereof, as a unit, to one ofa plurality of contact positions to generally conform the window portion27 to the biological tissue surface 21 to be ablated.

[0042] Accordingly, the microwave ablation instrument of the presentinvention enables manipulative bending of the antenna assembly toconform the window portion to the biological tissue surface to beablated. This ensures a greater degree of contact between the elongatedwindow portion and the targeted tissue. This is imperative to maintainthe radiation efficiency of the antenna, and thus, proper tuning formore efficient microwave transmission. Such manipulative bending alsosubstantially increases the versatility of the instrument since oneantenna assembly can be configured to conform to most tissue surfaces.

[0043] Briefly, the ablation instrument 20 includes a handle member 23coupled to the antenna assembly 26 through an elongated tubular shaft orsemi-rigid coaxial cable, hereinafter referred to as shaft 32. Bymanually manipulating the handle, the window portion 27 of the antennaassembly 26 may be oriented and positioned to perform the desiredablation. As mentioned, the shaft 32 is preferably provided a semi-rigidcoaxial cable or by a conductive material such as a metallic hypotubewhich is mounted to the components of the antenna assembly 26 throughbrazing paste, welding or the like, as will be discussed. Accordingly,when the shaft 32 is provided by the semi-rigid coaxial cable, thebraided outer conductor 29 of the semi-rigid coaxial cable 32,peripherally surrounding the center conductor 33, is preferablyconductively coupled to the outer conductor of the transmission line 25.Similarly, the inner conductor 33 of the semi-rigid coaxial cable 32 isconductively coupled to the inner conductor of the transmission line 25.

[0044] In contrast, when the shaft 32 is provided by the tubular, suchas a conductive hypotube, the solid cylindrical shell outer conductor 29thereof is preferably conductively coupled to the outer conductor of thetransmission line 25. In this configuration, the inner conductor and theinsulator of the transmission line extend through the cylindrical shellouter conductor 29 of the conductive hypotube 32 to provide the innerconductor 33 thereof. In this manner, the metallic hypotube itselffunctions as the outer conductor of the transmission line 25 forshielding along the length of the shaft.

[0045] Moreover, the shaft 32, whether the hypotube or the semi-rigidcoaxial cable, is preferably bendable and malleable in nature to enableshape reconfiguration to position the antenna assembly at a desiredorientation relative the handle. This permits the surgeon toappropriately angle the window portion toward the targeted region fortissue ablation. It will be appreciated, however, that the material ofthe shaft 32 is further sufficiently rigid so that the shaft is noteasily deformed during operative use. Such materials for the hypotube,for example, include stainless steel or aluminum having diametersranging from about 0.090 inches to about 0.200 inches with wallthickness ranging from about 0.010 inches to about 0.050 inches. Whenthe semi-coaxial cable is applied as the shaft 32, the outer diameter ofthe outer conductor ranges from about 0.090 inches to about 0.200inches, with wall thickness ranging from about 0.010 inches to about0.050 inches; while the inner conductor includes a diameter in the rangeof about 0.010 inches to about 0.050 inches.

[0046] The transmission line 25 is typically coaxial, and is coupled toa power supply (not shown) through connector 35 (FIG. 1). As bestillustrated in FIGS. 2 and 5-7, the microwave ablation instrument 20generally includes an elongated antenna wire 28 having a proximal endattached to center conductor 33 of transmission line 25. These linearwire antennas radiate a cylindrical electric field pattern consistentwith the length thereof It will be appreciated, however, that theantenna may be any other configuration, as well, such as a helical orcoiled antenna.

[0047] The electrical interconnection between the antenna wire 28 andthe distal end of the center conductor 33 may be made in any suitablemanner such as through soldering, brazing, ultrasonic welding oradhesive bonding. Moreover, the antenna wire 28 may be an extension ofthe center conductor of the transmission line itself which has theadvantage of forming a more rugged connection therebetween. Typically,the antenna wire 28 is composed of any suitable material, such as springsteel, beryllium copper, or silver-plated copper.

[0048] As will be discussed in greater detail below, the diameter of theantenna wire may vary to some extent based on the particular applicationof the instrument. By way of example, an instrument suitable for use inan atrial fibrillation application may have typical diameter in therange of approximately 0.005 to 0.030 inches. More preferably, thediameter of antenna wire may be in the range of approximately 0.013 to0.020 inches.

[0049] The antenna 28 is designed to have a good radiation efficiencyand to be electrically balanced. Consequently, the energy deliveryefficiency of the antenna is increased, while the reflected microwavepower is decreased which in turn reduces the operating temperature ofthe transmission line. Moreover, the radiated electromagnetic field issubstantially constrained from the proximal end to the distal end of theantenna. Thus, the field extends substantially radially perpendicularlyto the antenna and is fairly well constrained to the length of theantenna itself regardless of the power used. This arrangement serves toprovide better control during ablation. Instruments having specifiedablation characteristics can be fabricated by building instruments withdifferent length antennas.

[0050] Briefly, the power supply (not shown) includes a microwavegenerator which may take any conventional form. When using microwaveenergy for tissue ablation, the optimal frequencies are generally in theneighborhood of the optimal frequency for heating water. By way ofexample, frequencies in the range of approximately 800 MHz to 6 GHz workwell. Currently, the frequencies that are approved by the U.S. Food andDrug Administration for experimental clinical work are 915 MHz and 2.45GHz. Therefore, a power supply having the capacity to generate microwaveenergy at frequencies in the neighborhood of 2.45 GHz may be chosen. Aconventional magnetron of the type commonly used in microwave ovens isutilized as the generator. It should be appreciated, however, that anyother suitable microwave power source could be substituted in its place,and that the explained concepts may be applied at other frequencies likeabout 434 MHz, 915 MHz or 5.8 GHz (ISM band).

[0051] Referring back to FIGS. 1-5, the microwave ablation instrument 20of the present invention will be described in detail. Asabove-mentioned, the antenna wire 28, the shield device 30 and theinsulator 31 of the antenna assembly cooperate, as a unit, to enableselective manipulative bending thereof to one of a plurality of contactpositions to generally conform the window portion 27 to the biologicaltissue surface 21 to be ablated. Thus, FIGS. 3 and 4 illustrate twoparticular contact positions where the window portion 27 may beconfigured to maintain contact for substantially curvilinear tissuesurfaces 21. Consequently, due to the proper impedance matching betweenthe medium of the insulator 31 and that of the biological tissue,contact therebetween along the window portion 27 is necessary tomaintain the radiation efficiency of the antenna.

[0052] As above-mentioned, a flexible shield device 30 extendsubstantially along the length of the antenna substantially parallel tothe longitudinal axis of the antenna in a normal unbent position (shownin solid lines in FIG. 2 and phantom lines in FIG. 5). The shield device30 is formed and dimensioned to shield selected surrounding areasradially about the antenna wire 28 from the electric field radiallygenerated therefrom, while reflecting the field and permitting thepassage of the field generally in a predetermined direction toward thestrategically located window portion 27 of the insulator 31. As bestviewed in FIGS. 2, 7 and 9, the shield device 30 is preferablysemi-cylindrical or arcuate-shaped in the transverse cross-sectionaldimension to reflect the impinging field back toward the antennathereof.

[0053] Tissue ablation can thus be more strategically controlled,directed and performed without concern for undesirable ablation of otheradjacent tissues which may otherwise be within the electromagneticablation range radially emanating from the antenna. In other words, anyother tissues surrounding the peripheral sides of the antenna which areout of line of the window portion of the cradle will not be subjected tothe directed electric field and thus not be ablated. This ablationinstrument assembly is particularly suitable for ablation proceduresrequiring accurate tissue ablations such as those required in the MAZEIII procedure above-mentioned.

[0054] Briefly, it will be appreciated that the phrase “peripheral areaimmediately surrounding the antenna” is defined as the immediate radialtransmission pattern of the antenna which is within the electromagneticablation range thereof when the shield assembly is absent.

[0055] The shield device 30 is preferably composed of a highconductivity metal to provide superior microwave reflection. The wallsof the shield device 30, therefore, are substantially impenetrable tothe passage of microwaves emanating from the antenna 28 to protect abackside of the antenna assembly from microwave exposure. Morespecifically, when an incident electromagnetic wave originating from theantenna reaches the conductive shield device, a surface current isinduced which in turn generates a responsive electromagnetic field thatwill interfere with that incident field. Consequently, this incidentelectromagnetic field together with the responsive electromagnetic fieldwithin the shield device 30 of the antenna assembly 26 cancel and arethus negligible.

[0056]FIGS. 2 and 5 best illustrate that the shield device 30 ispreferably provided by a braided conductive mesh having a proximal endconductively mounted to the distal portion of the outer conductor of thecoaxial cable. This conductive mesh is preferably thin walled tominimize weight addition to the shield assembly yet provide theappropriate microwave shielding properties, as well as enablesubstantial flexibility of the shield device during bending movement.One particularly suitable material is stainless steel, for example,having mesh wires with a thickness in the range of about 0.005 inches toabout 0.010 inches, and more preferably about 0.007 inches.

[0057] As mentioned, an elongated microwave antenna normally emits anelectromagnetic field substantially radially perpendicular to theantenna length which is fairly well constrained to the length of theantenna wire regardless of the power used. However, to assure propershielding, the longitudinal length of the shield may be longer than andextend beyond the distal and proximal ends of the antenna wire 28.

[0058] To maintain the electromagnetic field characteristics of theantenna during operative use, even with a flexible antenna, it isimportant to maintain the position of a transverse cross-sectionalsegment of shield device 30 relative a corresponding transversecross-sectional segment of the antenna wire 28. Relative positionchanges between the segments may alter the radiation pattern and theradiation efficiency of the antenna. Accordingly, to stabilize thesetransverse cross-sectional segments of the shield device relative to thecorresponding transverse cross-sectional segments of the antenna wire28, the antenna assembly 26 includes the flexible insulator 31preferably molded over and disposed between the shield device 30 and theantenna wire 28.

[0059] The insulator 31 is preferably further molded to the distalportion of the metallic tubular shaft, and is preferably cylindricalshaped having an axis generally coaxial with that of the shield device30. The insulator 31 further performs the function of decreasing thecoupling between the antenna 28 and the flexible shield device 30.Should the antenna 28 be too close to the conductive shield device 30, astrong current may be induced at the surface thereof. This surfacecurrent will increase the resistive losses in the metal and thetemperature of the cradle device will increase. On the other hand,direct conductive contact or substantially close contact of the antennawith the metallic cradle device will cause the reflective cradle deviceto become part of the radiative structure, and begin emittingelectromagnetic energy in all directions.

[0060] The insulator 31 is therefore preferably provided by a good,low-loss dielectric material which is relatively unaffected by microwaveexposure, and thus capable of transmission of the electromagnetic fieldtherethrough. Moreover, the insulator material preferably has a lowwater absorption so that it is not itself heated by the microwaves.Finally, the insulation material must be capable of substantialflexibility without fracturing or breaking. Such materials includemoldable TEFLON®, silicone, or polyethylene, polyimide, etc.

[0061] In the preferred embodiment, the insulator 31 defines anelongated window portion 27 extending substantially adjacent andparallel to the antenna wire 28. Thus, as shown in FIGS. 5 and 7-9, alongitudinal axis of the antenna wire 28 is off-set from, but parallelto, the longitudinal axis of insulator 31 in a direction toward thewindow portion. This configuration positions the antenna wire 28actively in the window portion 27 to maximize exposure of the targetedtissue to the microwaves generated by antenna, as well as further spacethe antenna sufficiently away from the shield device to prevent theabove-mentioned electrical coupling.

[0062] In a normal unbent position of the antenna assembly 26 (shown insolid lines in FIG. 2 and phantom lines in FIG. 5), the window portion27 is substantially planar and rectangular in shape. Upon bendingthereof, however, the face of the window portion 27 can be manipulatedto generally conform to the surface of the tissue 22 to be ablated.Thus, a greater degree of contact of a curvilinear surface 21 of atissue 22 with full face of the window portion 27 is enabled. Theradiation pattern along the antenna, therefore, will not be adverselychanged and the antenna will remain tuned, which increases theefficiency and the penetration depth of the energy delivery into thetissue 22.

[0063] In accordance with the present invention, the window portion 27is strategically sized and located relative the shield device to directa majority of the electromagnetic field generally in a predetermineddirection. As best viewed in FIGS. 2, 5 and 7, the window portion 27preferably extends longitudinally along the insulator 31 in a directionsubstantially parallel to the longitudinal axis thereof The length ofthe ablative radiation is therefore generally constrained to the lengthof the antenna wire 28, and may be adjusted by either adjusting thelength of the antenna wire 28. To facilitate the coupling between thecoaxial cable and the antenna wire, the proximal end of the windowportion 27 generally extends proximally a little longer than theproximal end of the antenna 28 (about 2-5 mm). On the distal end,however, the window portion 27 is configured to approximate the lengthof the distal end of the shield device 30. Incidentally, as will bedescribed in greater detail below, the distal portion of the shielddevice 30 extends well beyond the distal end of the antenna toaccommodate for bending of the antenna assembly 26.

[0064]FIGS. 7 and 9 best illustrate that the radiation pattern of theelectromagnetic field delivered from the window portion 27 may extendradially from about 120° to about 180°, and most preferably extendradially about 180°, relative the longitudinal axis of the insulator.Thus, a substantial portion of the backside of the antenna is shieldedfrom ablative exposure of the microwaves radially generated by theantenna in directions substantially perpendicular to the longitudinalaxis thereof. The circumferential dimension of window portion 27, hence,may vary according to the breadth of the desired ablative exposurewithout departing from the true spirit and nature of the presentinvention. Moreover, while a small percentage of the electromagneticfield, unshielded by the shield device, may be transmitted out of othernon-window portions of the insulator, a substantial majority will betransmitted through the window portion. This is due to the impedancematching characteristics which are turned to contact between the tissueand the window portion.

[0065] Accordingly, the predetermined direction of the ablativeelectromagnetic field radially generated from the antenna may besubstantially controlled by the circumferential opening dimension, thelength and the shape of the window portion 27. Manipulating the shape ofthe antenna assembly 26 to conform the window portion generally to theshape of the targeted tissue surface, and positioning of window portion27 in the desired direction for contact with the tissue, thus, controlsthe direction of the tissue ablation without subjecting the remainingperipheral area immediately surrounding the antenna to the ablativeelectromagnetic field.

[0066] In a preferred embodiment of the present invention, an elongated,bendable, retaining member, generally designated 36, is provided whichis adapted for longitudinal coupling therealong to the insulator 31.Once the window portion 27 is manually manipulated for conformance tothe biological tissue surface to be ablated, this bendable retainingmember 36 functions to retain the insulator 31 in the one position foroperative ablation thereof. As best viewed in FIGS. 2, 5 and 7, theretaining member 36 is preferably positioned behind the shield device 30so as to be shielded from exposure to the microwaves transmitted byantenna 28. The retaining member preferably extends along the fulllength of the shield device in a direction substantially parallel to thelongitudinal axis of the insulator 31.

[0067] This retaining member 36 must be a ductile or bendable material,yet provide sufficient rigidity after being bent, to resist theresiliency of the insulator to move from a bent position (e.g., FIGS. 3and 4) back toward the normal position (FIG. 2). Moreover, both theretaining member 36 and the antenna wire 28 must not be composed of amaterial too rigid or brittle as to fracture or easily fatigue tearduring repeated bending movement. Such materials for the retainingmember include tin or silver plated copper or brass, having a diameterin the range of about 0.020 inch to about 0.050 inches.

[0068] In a preferred form, retaining member 36 is molded or embedded inthe moldable insulator. This facilitates protection of the retainingmember 36 from contact with corrosive elements during use. It will beappreciated, however, that retaining member 36 could be coupled to theexterior of the insulator longitudinally therealong.

[0069] As shown in FIGS. 2 and 5, a proximal portion of the retainingmember 36 is positioned adjacent and substantially parallel to a distalportion of the shaft 32. Preferably, the proximal portion of theretaining member 36 is rigidly affixed to the distal portion of theshaft 32 at a coupling portion 41 thereof to provide relative stabilitybetween the shaft and the antenna assembly 26 during bending movement.While such rigid attachment is preferably performed through soldering,brazing, or ultrasonic welding, the coupling could be provided by arigid, non-conductive adhesive or the like.

[0070] Preferably, the retaining member 36 is cylindrical-shaped, havinga substantially uniform transverse cross-sectional dimension. It will beappreciated, however, that other geometric transverse cross-sectionaldimensions may apply such as a rectangular cross-section. As shown inFIG. 9, this retaining member 36 is in the form of a thin metallic stripembedded atop the shield device 30. In this configuration, due to therelative orientation of the antenna and the shield device 30 bending invertical direction, will be permitted while movement in a lateralside-to-side direction will be resisted. Moreover, the retaining member36 may not be uniform in transverse cross-sectional dimension to permitvaried rigidity, and thus variable bending characteristics,longitudinally along the antenna assembly.

[0071] In another alternative configuration, the retaining member 36 maybe incorporated into the shield device or the antenna itself In eitherof these configurations, or a combination thereof, the shield deviceand/or the antenna must provide sufficient rigidity to resist theresiliency of the insulator 31 to move from the bent position (e.g.,FIGS. 3 and 4) back toward the normal position (FIG. 2).

[0072] In accordance with the present invention, the insulator 31defines a receiving passage 37 formed for sliding receipt of the antennawire 28 longitudinally therein during manipulative bending of theantenna assembly 26. As best viewed in FIGS. 5 and 6, this slidingreciprocation enables bending of the antenna assembly 26 withoutsubjecting the antenna 28 to compression or distension during bendingmovement of the antenna which may ultimately fatigue or damage theantenna, or adversely alter the integrity of the electromagnetic field.

[0073] Such displacement is caused by the bending movement of theantenna assembly pivotally about the retaining member 36. For example,as shown in FIG. 7, during concave bending movement (FIGS. 2 and 5) orconvex bending movement (FIG. 8) of the window portion 27 of the antennaassembly 26, the pivotal or bending movement will occur about thelongitudinal axis of the retaining member 36. Accordingly, upon concavebending movement of the window portion 27 (FIGS. 2 and 5), the length ofthe receiving passage 37 shortens. This is due to the fact that theinsulator 31 compresses at this portion thereof since the receivingpassage 37 is positioned along the radial interior of the retainingmember. Essentially, the radius of curvature of the receiving passage 37is now less than the radius of curvature of the outer retaining member36. However, the longitudinal length of the antenna 28 slideablyretained in the receiving passage 37 will remain constant and thus slidedistally into the receiving passage.

[0074] In contrast, upon convex bending movement of the window portion27 (FIG. 8), the length of the receiving passage 37 distends since thereceiving passage 37 will be positioned on the radial exterior of theretaining member 36. In this situation, the radius of curvature of thereceiving passage 37 will now be greater than the radius of curvature ofthe outer retaining member 36. Consequently, the distal end of theantenna slides proximally in the receiving passage 37.

[0075] Preferably, the diameter of the receiving passage is about 5% toabout 10% larger than that of the antenna wire 28. This assureuninterfered sliding reciprocation therein during bending movement ofthe antenna assembly 26. Moreover, the proximal end of the receivingpassage 37 need not commence at the proximal end of the antenna wire 28.For instance, since the displacement at the proximal portion of theantenna wire 28 is substantially less than the displacement of theantenna wire 28 at a distal portion thereof, the proximal end of thereceiving passage 37 may commence about 30% to about 80% from theproximal end of the antenna wire 28. The distal end of the receivingpassage 37, on the other hand, preferably extends about 30% to about 40%past the distal end of the antenna wire 28 when the antenna assembly isin the normal unbent position. As above-indicated, this space in thereceiving passage 37 beyond the distal end of the antenna 28 enablesreciprocal displacement thereof during concave bending movement.

[0076] To assure that the distal end of the antenna 28 does not piercethrough the relatively soft, flexible insulating material of theinsulator 31, during bending movement, the tip portion thereof may berounded or blunted. In another configuration, the receiving passage 37may be completely or partially lined with a flexible tube device 38(FIGS. 2 and 5-7) having a bore 39 formed and dimensioned for slidinglongitudinal reciprocation of the antenna distal end therein. The wallsof tube device 38 are preferably relatively thin for substantialflexibility thereof, yet provide substantially more resistance topiercing by the distal end of the antenna 28. Moreover, the materialcomposition of the tube device must have a low loss-tangent and lowwater absorption so that it is not itself affected by exposure to themicrowaves. Such materials include moldable TEFLON® and polyimide,polyethylene, etc.

[0077] Referring now to FIGS. 8 and 9, a restraining sleeve, generallydesignated 40, is provided which substantially prevents convex bendingmovement of the retaining member 36 at the proximal portion thereof. Atthis coupling portion 41, where the retaining member 36 and the shielddevice 30 are mounted to the distal portion of the shaft 32, repeatedreciprocal bending in the convex direction may cause substantial fatigueof the bond, and ultimately fracture. The restraining sleeve 40, thus,preferably extends longitudinally over the coupling portion 41 tomaintain the integrity of the coupling by preventing strains thereon.Essentially, such convex bending movement will then commence at aportion of the antenna assembly 26 distal to the coupling portion.

[0078] The restraining sleeve 40 includes an arcuate shaped base portion42 removably mounted to and substantially conforming with thecircumferential cross-sectional dimension of the proximal portion of theinsulator 31 (FIG. 9). The base portion 42 is rigidly affixed to theantenna assembly and/or the shaft to provide protective stability overthe coupling portion 41.

[0079] A finger portion 43 extends distally from the base portion 42 ina manner delaying the commencement of convex bending of the antennaassembly to a position past the distal end of the finger portion 43.Consequently, any strain upon the coupling portion 41 caused by convexbending movement of the antenna assembly is eliminated.

[0080] In another embodiment of the present invention, the microwaveablation instrument 20 includes an elongated grip member 45 having adistal grip portion 46 and an opposite proximal portion 47 coupled to adistal portion of the antenna assembly 26. As best illustrated in FIGS.10 and 11, the grip member 45 and the handle member 23 of the ablationinstrument 20 cooperates to selectively bend the flexible antennaassembly 26 and selectively urge the window portion 27 into abuttingcontact with the biological tissue surface to be ablated. For example,this application is particularly useful when the targeted tissue surfaceis located at a rear portion of an organ or the like. FIG. 11illustrates that, during open procedures, the elongated grip member 45may be passed around the backside of the organ until the window portion27 of the antenna assembly is moved into abutting contact with thetargeted tissue surface 21. Subsequently, the handle member 23 at oneend of the ablation instrument, and the grip member 45 at the other endthereof are manually gripped and manipulated to urge the window portion27 into ablative contact with the targeted tissue surface.

[0081] This configuration is beneficial in that the window portion 27 isadapted to conform to the tissue surface upon manual pulling of the gripmember 45 and the handle member 23. As the flexible antenna assembly 26contacts the targeted tissue 22, the window portion 27 thereof is causedto conform to the periphery of the tissue surface. Continuedmanipulation of the grip member 45 and the handle member 23 further urgebending contact. Accordingly, this embodiment will not require aretaining member for shape retention.

[0082] The elongated grip member 45 is provided by a substantiallyflexible rod having a diameter smaller than the diameter of theinsulator 31. Such flexibility enables manipulation of the rod toposition its distal end behind a targeted biological tissue 22. Once thedistal grip portion 46 of the grip member 45 is strung underneath organ22 or the like, the distal grip portion 46 may be gripped to pull theantenna assembly 26 behind the organ 22 for ablation of the targetedtissue.

[0083] It will be appreciated, however, that the rod 45 should not besubstantially more flexible than that of the antenna assembly. Thisassures that the window portion 27 of the insulator 31 will be caused toconform to the curvilinear surface of the targeted tissue 22, as opposedto the mere bending of the flexible rod 45. Such materials for theflexible rod 45 includes Pebax filled with silicone and polyethylene,polyurethane, etc.

[0084] To mount flexible rod 48 to the ablation instrument 20, theantenna assembly 26 includes a mounting portion 48 extending distallyfrom the insulator 31. This mounting portion 48 is preferably integrallyformed with the insulator 31 and is of a sufficient length to enable theproximal portion of flexible rod 45 to be integrally molded theretowithout interference with the shield device 30 and/or the antenna wire28.

[0085] In the preferred embodiment, a longitudinal axis of the flexiblerod 45 is off-set from the longitudinal axis of the insulator 31 in thedirection toward the window portion 27. As viewed in FIG. 11, thisoff-set preferably positions the longitudinal axis of the flexible rodproximately in co-axial alignment with the antenna. This arrangementfacilitates alignment of the window portion 27 against the targetedtissue 22 as the grip member 45 and the handle member 23 are manipulatedto conform the window portion 27 with and against the tissue surface 21.Due to the off-set nature of the flexible rod 45, when the antennaassembly and the rod are tightened around the biological tissue 22, theantenna assembly 26 is caused to rotate about its longitudinal axistoward an orientation of least resistance (i.e., a position where theflexible rod 45 is closest to the biological tissue 22).

[0086] Additionally, as shown in FIG. 12, the handle member 23 may beelongated and substantially flexible in a manner similar to theelongated grip member 45. In another embodiment of the presentinvention, the handle member 23 includes a proximal grip portion 50 andan opposite distal portion 51 coupled to a proximal portion of theantenna assembly 26. Thus, the flexible handle member 23 and theflexible grip member 45 cooperate to selectively bend the flexibleantenna assembly 26 and selectively urge the window portion 27 intoabutting contact with the biological tissue surface to be ablated. Asanother example, this application is particularly useful for creatinglong continuous linear lesions (E.g., to enclose the pulmonary veinswhen treating atrial fibrillation or the like). The flexible handlemember 23 at one end of the ablation instrument, and the flexible gripmember 45 at the other end thereof are manually gripped and manipulatedto urge the window portion 27 into ablative contact with the targetedtissue surface. This can be performed by simply sliding the antennaassembly 26 by pulling either the flexible grip member 45 or theflexible handle member 23 to position the widow portion 27 against thetissue. Moreover, this can be used to slightly overlap the lesions togenerate a long continuous lesion without gaps. easily end the targetedtissue surface is located at a rear portion of an organ or the like.

[0087] The elongated flexible handle member 23 is preferably provided bya substantially flexible coaxial cable appropriately coupled to thetransmission line. In some instances, the handle member 23 may simply bean extension of the transmission line.

[0088] Preferably, the flexible coaxial cable handle member 23 iscovered by a plastic sleeve such as Pebax, PE Polyolifin, etc. Such dualflexibility enables increased manipulation of both the gripping memberand the handle member. To mount flexible handle member 23 to the antennaassembly 26, the distal portion thereof is preferably integrally formedwith the insulator 31

[0089] Similar to the gripping member 45, a longitudinal axis of theflexible handle member 23 is off-set from the longitudinal axis of theinsulator 31 in the direction toward the window portion 27. As viewed inFIG. 12, this off-set, together with the same off-set of the grippingmember, preferably positions the longitudinal axis of the handle memberproximately in co-axial alignment with the antenna. This arrangementfacilitates alignment of the window portion 27 against the targetedtissue 22 as the grip member 45 and the handle member 23 are manipulatedto conform the window portion 27 with and against the tissue surface 21.Due to the off-set nature of the flexible rod 45, when the antennaassembly and the rod are tightened around the biological tissue 22, theantenna assembly 26 is caused to rotate about its longitudinal axistoward an orientation of least resistance (i.e., a position where theflexible rod 45 is closest to the biological tissue 22).

[0090] In still another aspect of the present invention, a method isprovided for treatment of a heart including providing a microwaveablation instrument 20 having a flexible antenna assembly 26 defining awindow portion 27 enabling the transmission of a directed electric fieldtherethrough in a predetermined direction. By selectively bending theflexible antenna assembly 26 to one of a plurality of contact positions,the window portion 27 can be generally conformed to the shape of thetargeted biological tissue 22 surface to be ablated. The method furtherincludes manipulating the ablation instrument 20 to strategicallyposition the conformed window portion 27 into contact with the targetedbiological tissue surface 21; and generating the electric fieldsufficiently strong to cause tissue ablation to the targeted biologicaltissue surface 21.

[0091] More preferably, this method is directed toward medicallyrefractory atrial fibrillation of the heart. By repeating the bending,manipulating and generating events, a plurality of strategicallypositioned ablation lesions can be accurately formed in the heart.Collectively, these lesions are formed to create a predeterminedconduction pathway between a sinoatrial node and an atrioventricularnode of the heart, or to divide the left and/or right atrium in order toavoid any reentry circuits.

[0092] These techniques may be preformed while the heart remainsbeating, such as in a minimally invasive heart procedure, while theheart is temporarily arrested, such as when the heart is stabilized forabout 20 or 30 seconds during a cabbage procedure, or while the heart isarrested, such as in an open heart surgery. Moreover, these proceduresmay be applied to ablate the endocardium as well as the epicardium inorder to treat atrial fibrillation. throughout the bending, manipulatingand generating events. Moreover, the repeated events of bending,manipulating and generating are applied in a manner isolating thepulmonary veins from the epicardium of the heart.

[0093] Although only a few embodiments of the present inventions havebeen described in detail, it should be understood that the presentinventions may be embodied in many other specific forms withoutdeparting from the spirit or scope of the inventions. Particularly, theinvention has been described in terms of a microwave ablation instrumentfor cardiac applications, however, it should be appreciated that thedescribed small diameter microwave ablation instrument could be used fora wide variety of non-cardiac ablation applications as well.

[0094] It should also be appreciated that the microwave antenna need notbe a linear antenna. The concepts of the present invention may beapplied to any kind of radiative structure, such as a helical dipoleantenna, a printed antenna, a slow wave antenna, a lossy transmissionantenna or the like. Furthermore, it should be appreciated that thetransmission line does not absolutely have to be a coaxial cable. Forexample, the transmission line may be provided by a stripline, amicrostrip line, a coplanar line, or the like.

1. A method of ablating tissue at a target tissue site, comprising thesteps: providing a flexible ablation device defining an outer ablationsurface and comprising a means for directionally controlling ablationenergy emitted therefrom; manipulating the distal portion of theablation device to generally conform the ablation surface to a tissuesurface at the target tissue site; applying ablation energy sufficientto ablate tissue at the target tissue site.
 2. The method of claim 1,wherein the ablation device comprises at least one ablation element. 3.The method of claim 2, wherein the at least one ablation element is anantenna.
 4. The method of claim 1, wherein the ablation energy is one ormore energies from the group consisting of: radiofrequency, microwave,and cryogenic.
 5. The method of claim 1, wherein the means fordirectionally controlling the ablation energy is a shield device adaptedto direct the ablation energy in a single direction along a longitudinalaxis of the ablation device, whereby the step of applying ablationenergy results in the creation of a continuous lesion.
 6. The method ofclaim 6, wherein the step of applying ablation energy results in theisolation of at least one pulmonary vein from the epicardial surface ofa patient's heart.
 7. A method for treatment of a heart comprising:providing an ablation instrument having a flexible antenna assemblydefining a window portion enabling the transmission of a directedelectric field therethrough in a predetermined direction; selectivelybending the flexible antenna assembly to one of a plurality of contactpositions to generally conform the shape of said window portion to thetargeted biological tissue surface to be ablated; manipulating theablation instrument to strategically position the conformed windowportion into contact with the targeted biological tissue surface; andgenerating the electric field sufficiently strong to cause tissueablation to the targeted biological tissue surface.
 8. The method ofclaim 7, wherein said flexible antenna assembly includes: a flexibleantenna for radially generating the electric field; a flexible shielddevice coupled to said antenna to substantially shield a surroundingarea of the antenna from the electric field radially generated therefromwhile permitting a majority of the field to be directed generally in thepredetermined direction; and a flexible insulator disposed between theshield device and the antenna, and defining said window portion enablingthe transmission of the directed electric field in the predetermineddirection.
 9. The method of claim 8, further including: repeating thebending, manipulating and generating events to form a plurality ofstrategically positioned ablation lesions.
 10. The method of claim 9,wherein the lesions are formed to create a predetermined conductionpathway in the muscular tissue wall of the targeted biological tissueand/or to divide the left and/or right atria to substantially preventreentry circuits.
 11. The method of claim 8, further including: anelongated, bendable, retaining member coupled longitudinally therealongto said insulator in a manner enabling the insulator to retain the onecontact position after manipulative bending thereof for said conformanceof the window portion to the biological tissue surface to be ablated.12. The method of claim 1, wherein said retaining member is embedded inthe flexible insulator.
 13. The method of claim 7, wherein the heartremains beating throughout the bending, manipulating and generatingevents.
 14. The method of claim 7, further including: arresting thepatient's heart.
 15. The method of claim 7, further including:temporarily arresting the patient's heart.
 16. The method of claim 7,wherein said ablation instrument is a microwave ablation instrument. 17.A method for ablating medically refractory atrial fibrillation of theheart comprising: providing an ablation instrument having a flexibleantenna assembly adapted to generate an electric field sufficientlystrong to cause tissue ablation, said antenna assembly defining a windowportion enabling the transmission of the electric field therethrough ina predetermined direction; selectively bending and retaining theflexible antenna assembly in one of a plurality of contact positions togenerally conform the shape of said window portion to the targetedbiological tissue surface to be ablated; manipulating the ablationinstrument to strategically position the conformed window portion intocontact with the targeted biological tissue surface; and forming anelongated lesion in the targeted biological tissue surface through thegeneration of the electric field by the antenna assembly.
 18. The methodof claim 17, wherein said flexible antenna assembly includes: a flexibleantenna for radially generating the electric field; a flexible shielddevice coupled to said antenna to substantially shield a surroundingarea of the antenna from the electric field radially generated therefromwhile permitting a majority of the field to be directed generally in thepredetermined direction; and a flexible insulator disposed between theshield device and the antenna, and defining said window portion enablingthe transmission of the directed electric field in the predetermineddirection.
 19. The method of claim 18, further including: repeating thebending, manipulating and generating events to form a plurality ofstrategically positioned ablation lesions and/or to divide the leftand/or right atria to substantially prevent reentry circuits.
 20. Themethod of claim 19, wherein the lesions are formed to create apredetermined conduction pathway between a sinoatrial node and anatrioventricular node of the heart.
 21. The method of claim 19, whereinsaid repeating the bending, manipulating and generating events areapplied in a manner isolating the pulmonary veins from the epicardium ofthe heart.
 22. The method of claim 18, further including: an elongated,bendable, retaining member coupled longitudinally therealong to saidinsulator in a manner enabling the insulator to retain the one contactposition after manipulative bending thereof for said conformance of thewindow portion to the biological tissue surface to be ablated.
 23. Themethod of claim 22, wherein said retaining member is embedded in theflexible insulator.
 24. The method of claim 17, wherein the heartremains beating throughout the bending, manipulating and generatingevents.
 25. The method of claim 23, wherein said biological tissuesurface includes the epicardium of the heart during a minimally invasiveheart procedure.
 26. The method of claim 17, further including:arresting the patient's heart.
 27. The method of claim 17, furtherincluding: temporarily arresting the patient's heart.
 28. The method ofclaim 26, wherein said biological tissue surface includes theendocardium of one of the left atrium and the right atrium during anopen-heart procedure.
 29. The method of claim 17, wherein said ablationinstrument is a microwave ablation instrument.
 30. The method of claim17, wherein said ablation instrument includes an elongated flexiblegripping member having a distal grip portion and an opposite proximalportion coupled to a distal portion of said antenna assembly, and ahandle member coupled to a proximal portion of said antenna assembly;and said manipulating includes manually gripping said flexible grippingmember and said handle member to cooperatively and selectively bend saidantenna assembly to selectively urge the window portion in abuttingcontact with the biological tissue surface to be ablated.
 31. The methodof claim 30, wherein said handle member is a flexible elongated member.